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Comparative Assessment of Forested and Cultivated Soils for Sustainable Crop Production in Mubi Environment, Northeastern Nigeria.

Byline: I.J. TEKWA, B.H. USMAN AND H. YAKUBU - E-mail: johntekwa@gmail.com

ABSTRACT

An assessment of physico-chemical properties of 22 soils samples (at composite surface and horizon depths) from forested and cultivated fields within Mubi, Nigeria, was conducted between June and August, 2008. There was a significant difference (Pless than0.05) between the compared soil properties. Both soil types were sandy clay loam textured with moderate compactions (1.56/1.50 Mg m-1) and porosities (41.23/43.21%) marked by slightly saline (0.17/0.16 dS m-1) conditions. The soils were slightly acidic (pH 6.45) and alkaline (pH 7.46) in forested and cultivated soils, respectively. Total N (0.16/0.05%) and organic matter (2.09/1.13%) contents, respectively had medium and low rates in forested and cultivated soils. The available K and Mg were high, while available P and exchangeable Na had medium and low rates in both soil types.

The exchangeable Ca and CEC (cation exchange capacity) were moderate in forested and low in cultivated soils, while the PBS had very high (93.66/91.70%) concentrations in the soil types. Generally, the soils still pose good potentials for sustainable crop production, particularly the forested soil that indicated high nutrient edge over cultivated soils. It is recommending that the forested fields may be converted into arable land uses in the study area. (c) Friends Science Publishers

Key Words: Assessment; Forested; Cultivated; Soil potentials; Sustainable; Crop production; Nigeria

INTRODUCTION

The heterogeneous nature of land makes it variable in both physical and chemical compositions that largely depend on the nature of soil and pattern of land use. This difference in land application generates variation in the agricultural production potentials and system of crop management (Gliessman, 1990; Baumer, 1990; Mengel and Kirkby, 2006). Forest lands consist of trees and shrubs of modest heights that competitively utilize oxygen, water and soil nutrients to attain desired maturity compared to most depleted cultivated soils (Vergara and Nair, 1995). Several years of land cultivation could lead to sharp decline in nutrient reserves that are often reclaimed through bush fallow and other soil fertility enrichment options, such as planting trees, shrubs and green manure crops on the degrading lands (Montagnini, 1990; Vergara and Nair, 1995; Mengel and Kirkby, 2006).

Forest vegetation conserves soil properties through organic matter additions and soil aggregate stability against erosion devastation, as well as protecting soils from direct impacts of rain splash and solar radiations compared to cultivated soils (Vergara and Nair, 1995; Brady and Weil, 2002; Mengel and Kirkby, 2006). Plant roots generally promote stable granulation of the surface aggregates, thereby improving soil porosity and infiltration capacities (King, 1997; Brady and Weil, 2002). Continuous cultivation of farm lands appears necessary for the production of food crops, fiber and employment sources to most farmers. In recent years, over-cultivation ignited from intensive land uses beyond the threshold limits of soil natural fertility to compensate for the nutrient depletions, have necessitated supplemental soil fertilization and nutrient recycling (Dahl, 1980; Bottrell, 1998) thereby, predisposing soils to limited fertility statuses (Mengel and Kirkby, 2006).

This continuous cultivation practices further exposes soils to variable degradation factors. The amount of harm done often depends on the system of practices adopted and how the farmer handles his land and the type of crop/s grown (Parkinson, 1993; Clarke, 1995).

Mubi environment is one area that is still afflicted by erosion hazards with sparse tree vegetations, routinely subjected to intensive soil cultivation and marked by sharp nutrient depletion. This study was therefore, designed to asses the fertility potentials of the forested over the cultivated soils towards recommending suitable land management practices compatible to the study area.

Methodology

Study area: Mubi local government area is situated in the northeastern part of Adamawa state and located between latitudes 9o 26'' and 10o 11'' N and between longitudes 13o 10'' and 13o 44'' E. It has a land area of 506.40 km2 and a population size of 759,045 with a density of 160.5 people per square kilometer. The local government shares boundaries with Michika to the North, Askira-Uba to the West and Hong local government to the South. It also shares international boundary with the Republic of Cameroon to the East.

The climate of the area is characterized by alternating dry and wet seasons. The rain lasts from April to October with a mean annual rainfall ranging from 700 mm to 1,050 mm (Udo, 1970; Adebayo, 2004). The vegetation is of typical Sudan Savannah, which implies grassland interposed by shrubs and few trees mostly, acacia, locust-beans and eucalyptus trees among others (Adebayo, 2004; Tekwa and Usman, 2006). The land use types are mainly arable farming and livestock production threatened by soil erosion at varying extent of devastations, from sheet and rill erosion to the spectacular gully erosion known for colossal loss of soil and soil nutrients (Tekwa et al., 2006).

Field study: Two land use types (forests and cultivated) were investigated in Mubi area between June and August, 2008. The forested vegetation (Yellow-Cassia) and cultivated sites with establishment history of between one and two decades were sited and from, which the soils were sampled for this study.

Soil sampling: Soil samples at the surface (0-15 cm) and sub surface (15-30 cm) depths and from soil pedons were collected using a bucket soil-auger and core samplers, respectively. Two composite samples were collected at the top (0-15 cm) and sub-surface (15-30 cm) soil depths each, while the pedogenic samples were collected at observed horizon depths in each soil pedon dug on both fields. A total of 22 composite soil samples were collected, air dried, crushed and sieved through a 2 mm sieve and kept in well labeled polythene bags for routine laboratory analysis.

Determination of soil physical properties: The determinations of soil physical properties were conducted in the laboratory. The particle size distribution (PSD) was determined using Bouyoucous hydrometer method (Trout et al., 1987) in sequence, the textural class of the soil was determined by subjecting the obtained particle size distribution to Marshall's textural triangle. The bulk density was determined by clod method, while the water holding capacity was determined by gravimetric water content of a given quantity of soil fully saturated with water.

Determination of soil chemical properties: The soil pH was measured in a 1:2.5 soil to water suspension ratio with the use of a glass electrode pH meter. The electrical conductivity (EC) of a saturation extract was determined in sequence alongside the pH in same suspension. The organic carbon (OC) was determined using potassium dichromate wet-oxidation method of Walkley and Black (1934), from which the soil organic matter was obtained by multiplying the OC with a conversion factor of 1.724. Total nitrogen (N) was determined by Kjedahl method, while the available phosphorus (P) by Bray 1 method (Bray and Kurtz, 1945; Wolf, 2003). The available potassium (K) and sodium (Na) were determined by flame photometry (Jackson, 1965; Wolf, 2003). The exchangeable calcium (Ca) and the magnesium (Mg) were determined by tetrimetric method, while the cation exchange capacity (CEC) and the total exchangeable bases (TEB) were computed from the analyzed result of the soil bases.

Data analysis: The student t-test was used to compare some of the properties analyzed in both the forested and cultivated soils.

RESULTS AND DISCUSSION

The vegetation of the study sites were made of dense yellow-cassia tree vegetation established over two decades on the forested field, while arable crops (e.g., maize, cowpea, sorghum, rice, millet and groundnut) were grown on the cultivated field having a land use history of over a decade. Both fields occupied almost flat laying topography. Presented in Table I is the result of investigation of the soil physical properties of both the forested and cultivated soils, which indicated a predominance of sand skins constituting the observed sandy clay loam soil textures. The soils exhibited differing soil structures of between sub-angular blocky and massive structural stabilities, with moderate compactions in both the forested (1.49-1.64 Mg m-3) and cultivated (1.45-1.55 Mg m-3) soils (Table III). The soil porosity estimates of both soil types were medium ranging (38.11-45.28%).

These estimates are comparable with the earlier findings (sandy clay loam textures, massive soil structures, moderate porosities and soil compactions) reported by Tekwa et al. (2006) for soils in the same environment.

Results on investigation of the soil chemical properties is presented in Table II, it revealed that the soil reaction (pH) differed among the soils, the forested soil was slightly acidic (pH 6.45), while the cultivated soil was slightly alkaline (pH 7.46) in reactions. These ranges are within the adequate pH (6.5-8.5) for most crop production (Wolf, 2003). However, both soil types were only slightly saline/acidic (Table III), suggestive of the soils as still un-saturated with harmful salts (e.g., Sodium), which limits irrigation farming potentials (Brady and Weil, 2002; ICAR, 2006). The soil organic matter (OM) content ranged lower (0.90-1.36%) in cultivated soil and with medium ranges (1.85-2.50%) in forested soils. Further statistical test (t-test) indicated a significant difference (Pless than0.05) between the OM content of both soil types (Table IV).

This low ranges of OM content in the cultivated soils appeared similar to the range (0.27-1.05%) earlier reported by Tekwa et al. (2006) for some locations within same Mubi area, while the OM content of the forested soils compared slightly higher than

Table I: Soil physical properties

Soil Sample Type###Sampling Depth###Particle Size Distribution (%)###Soil Texture###Bulk Density###Porosity###

###(cm)###Sand###Silt###Clay###(Class)###(Mg/m3)###(%)###

Forested Soil###

Surface samples TS1###0-15###63-70###14.25###22.05###Sandy clay loam###1.52###42.67###

SS1###15-30###53.70###21.75###24.55###Sandy clay loam###1.58###40.38###

TS2###0-15###64.60###13.50###21.90###Sandy clay loam###1.49###43.77###

SS2###15-30###55.40###20.80###23.80###Sandy clay loam###1.64###38.11###

Pedogenic samples###0-16###58.70###19.25###22.05###Sandy clay loam###1.45###45.28###

###16-27###46.20###19.25###34.55###sandy clay###1.66###37.36###

###27-67###36.20###24.55###39.25###clay loam###1.66###37.36###

###67-96###26.20###32.05###41.76###clay loam###1.68###36.60###

###96-128###38.70###27.05###34.25###clay loam###1.65###37.74###

Cultivated Soil###128-200###38.70###26.75###34.55###clay loam###1.67###36.98###

Surface samples TS1###0-15###53.70###16.55###29.55###sandy clay loam###1.45###45.28###

SS1###15-30###66.20###11.75###22.05###Sandy clay loam###1.54###41.89###

TS2###0-15###54-25###17.10###28.65###Sandy clay loam###1.48###44.15###

SS2###15-30###65.50###12.50###22.00###Sandy clay loam###1.55###41.51###

Pedogenic samples###0-9###61.20###16.75###22.05###Sandy clay loam###1.45###45.28###

###9-15###66.20###13.80###20.00###sandy loam###1.64###38.11###

###15-22###66.20###15.50###18.30###sandy loam###1.59###40.00###

###22-30###43.70###19.25###37.05###sandy clay###1.62###38.87###

###30-55###81.20###7.05###17.75###loamy sand###1.54###41.89###

###55-68###31.20###29.25###39.55###clay loam###1.45###45.28###

###68-78###58.70###19.25###22.05###sandy clay loam###1.46###44.91###

###78-135###21.20###34.25###44.55###clay loam###1.45###45.28###

Key: TS = top surface; SS = sub-surface###

Table II: Soil chemical properties###

Soil sample###Sampling###Soil pH 1:2.5###EC###OM###Total N###Ave P###Exch.###Exch.###Exch.###Exch.###Exch.###CEC###PBS###

Type###Depth (cm)###(soil:water) dS m-1)###(%)###(%)###(ppm)###K###Na###Ca###Mg###(Al+H)###(%)###

###(Cmol (+)/kg###

Forested soil###

Surface TS1###0-15###7.660###0.024###1.983###0.167###7.700###0.627###0.274###6.008###5.800###0.900###13.609###93.387###

samples SS1###15-30###5.290###0.273###1.845###0.146###6.350###0.550###0.226###4.810###4.200###0.600###10.390###94.225###

TS2###0-15###5.500###0.025###2.500###0.160###7.500###0.650###0.301###5.100###6.500###0.950###13.500###92.963###

SS2###15-30###7.300###0.350###2.050###0.150###7.800###0.680###0.365###4.550###5.500###0.700###11.800###94.068###

Pedogogic###

Samples###0-16###7.520###0.163###1.917###0.020###8.430###0.648###0.278###3.806###5.600###0.500###10.830###95.383###

###16-27###8.580###0.124###1.412###0.013###12.650###0.588###0.226###4.810###4.000###1.000###10.620###90.584###

###27-67###7.130###0.103###0.976###0.016###9.100###0.422###0.218###6.613###3.800###0.600###11.653###94.851###

###67-96###6.940###0.088###0.505###0.013###11.250###0.550###0.222###4.008###3.600###0.800###9.18###91.285###

###96-128###8.250###0.107###0.438###0.012###16.800###0.499###0.287###6.012###4.000###0.900###11.698###92.306###

Cultivated soil###128-200###7.450###0.123###0.202###0.008###5.600###0.422###0.252###4.609###3.000###0.600###8.883###93.246###

Surface TS1###0-15###6.970###0.158###1.362###0.124###9.150###0.640###0.196###5.812###5.200###0.900###12.748###92.940###

samples SS1###15-30###7.170###0.158###0.941###0.014###7.780###0.346###0.187###3.006###6.200###0.800###10.539###92.409###

TS2###0-15###6.980###0.156###1.301###0.105###9.200###0.660###0.205###3.950###4.100###0.880###9.800###91.020###

SS2###15-30###7.500###0.155###0.902###0.050###8.100###0.450###0.210###3.100###3.800###0.800###8.360###90.431###

Pedogogic###

Samples###0-9###7.040###0.135###1.581###0.165###11..920###0.397###0.283###3.407###4.400###0.500###8.987###94.436###

###9-15###7.380###0.154###1.075###0.014###8.450###0.448###0.205###4.008###2.400###0.800###7.861###89.823###

###15-22###8.310###0.143###0.772###0.014###14.000###0.461###0.226###4.008###2.600###1.200###8.495###85.874###

###22-30###7.370###0.154###0.976###0.016###17..500###0.512###0.248###4.409###2.600###0.600###8.369###92.831###

###30-55###7.510###0.159###0.537###0.012###12.600###0.294###0.200###3.006###5.00###0.800###9.300###91.398###

###55-68###6.810###0.045###1.681###0.015###18.200###0.397###0.283###3.006###1.200###0.700###5.586###87.469###

###68-78###6.720###0.073###1.377###0.150###13..300###0.589###0.239###5.611###1.400###1.000###8.839###88.687###

###78-135###6.620###0.044###1.748###0.017###20.300###0.358###0.357###3.808###2.800###0.800###8.123###90.151###

Key: Exch = exchangeable, EC = Electrical Conductivity, OM = Organic Matter, N= Nitrogen, P = Phosphorus, K = Potassium, Na = Sodium, Ca = Calcium, Mg = Magnesium, Al = Aluminium, H = Hydrogen, CEC = Cation Exchange Capacity, PBS = Percentage Base Saturation

the range (1.23-2.46%) reported by Ekwue and Tashiwa (1992) for some soil sites in the same environment. The low OM values observed in the cultivated soils could probably be due to the sparse vegetation, overgrazing and marginal land usage as influenced by human activities (Tekwa and Belel, 2008).

The result on statistical contrasts between the mean OM content of the forested and cultivated surface soils is presented in Table IV. The student t-test showed that the calculated t-value (22.803) is greater than t-critical (2.447), then Ho is rejected, implying that there exist a significant difference (Pless than0.05) between the OM content of forested and cultivated soils, suggestive of higher fertility rates in forested than cultivated soils as observed in this study.

Table III: The soil physico-chemical characteristics and rates within plant rooting depth (0-30 cm)

Soil properties###Forested soil###Cultivated soil###

###Units###Ranges###Mean content###Ratings###Ranges###Mean Content###Ratings###

Particle Size Distribution###Physical Properties###

Sand###%###53.70 - 64.60###59.35###Coarse textured###54.25-66.20###51.91###

Silt###%###13.50 - 21.75###17.58###11.75-17.10###14.48###Medium textured###

Clay###%###21.90 - 24.55###23.08###22.00-29.55###25.56###

Soil texture###Class###Sandy clay loam###Sandy clay loam###Sandy clay loam###Sandy clay loam###Sandy clay loam Sandy clay loam###

Soil structure###Class###Sbk/m###Sbk###Sbk###Sbk/m###Sbk/m###Massive###

Bulk density###Mgm-3###1.49 - 1.64###1.56###Moderate###1.45-1.55###1.50###Moderate###

###compaction###compaction###

Soil porosity###%###38.11 - 43.77###41.23###Medium###41.51-45.28###43.21###Medium###

###Chemical properties###

Soil reaction (pH)###-###5.29 - 7.66###6.45###Slightly acidic###6.97-7.50###7.46###Slightly alkaline###

Electrical conductivity (EC)###dSm-1###0.024 - 0.350###o.17###Slightly saline###0.155-0.158###0.16###Slightly saline###

Organic matter (O.M)###%###1.845 - 2.500###2.09###Medium###0.902-1.362###0.13###Low###

Total Nitrogen (N)###%###0.146 - 0.167###0.16###Medium###0.014-0.105###0.05###Low###

Avail. Phosphorus (P)###Ppm###6.350 - 7.800###7.35###Medium###7.780-9.200###8.56###Medium###

Exch. Potassium (K)###Cmol(+)/kg###0.550 - 0.680###0.53###High###0.346-0.660###0.63###High###

Exch. Sodium (Na)###Cmol(+)/kg###0.220 - 0.365###0.29###Low###0.187-0.210###0.20###Low###

Exch. Calcium (Ca)###Cmol(+)/kg###4.550 - 6.008###5.12###Moderate###3.006-5.812###3.97###Low###

Exch. Magnesium (Mg)###Cmol(+)/kg###4.200 - 6.500###5.50###High###3.800-.6.200###4.83###High###

Percentage Base saturation (PBS)###%###92.960 - 94.225###93.66###Very high###90.431-92.940###91.70###Very high###

Cation Exchange Capacity###Cmol(+)/kg###10.390 -13.609###12.33###Moderate###8.360-12.748###10.36###Low###

Key: Exch = exchangeable, Sbk = sub-angular blocky, m = massive###

Table IV: Student t-test of the mean OM content of the forested and cultivated surface soils###

S/N###Soil type###[?]###X###SS###N Degree of freedom (df)###t-calculated###t-critical###Remark###

1###Forested###7.77###1.943###15.783###4###

2###Cultivated###4.50###1.125###5.233###4###6###22.803###2.447###Reject Ho###

Tested at 0.05 level of significance; Legend: [?] = Sum of CEC Content; X = Mean of CEC Content; N = Number of observation; SS = Sum of Squares###

Table V: Student t-test of the mean CEC values of the forested and cultivated surface soils###

Soil type###[?]###X###SS###N###Degree of freedom (df) t-calculated###t-critical###Remark###

Forested###49.30###12.33###614.67###4###

Cultivated###41.45###10.36###439.58###4###6###2.763###2.447###Reject Ho

Tested at 0.05 level of significance; Legend: [?] = Sum of CEC Content; X = Mean of CEC Content; N = Number of observation; SS = Sum of Squares

Table V: Student t-test of the mean CEC values of the forested and cultivated surface soils

Soil type [?] X SS N Degree of freedom (df) t-calculated t-critical Remark

Forested 49.30 12.33 614.67 4

Cultivated 41.45 10.36 439.58 4 6 2.763 2.447 Reject Ho

Tested at 5% level of significance

Several changes in soil quality especially OM content occur, when virgin soil is routinely cultivated (Saviozzi et al., 2001).

The total soil nitrogen (N) content was low ranging (0.02-0.12%) on cultivated field and medium ranging (0.12-0.17%) on the forested field. Both N ranges in this study compared lower than the range (0.14-0.21%) earlier observed in some soil locations in the same environment (Tekwa et al., 2006). This low N estimates could likely be due to N mobility in tropical soils (Sanchez and Leaky, 1997) or perhaps due to poor N returning capacities of yellow-cassia tree vegetations with prolonged N uptakes by the plants without proper compensations with N enriching fertilizer sources (Ekwue and Tashiwa, 1992; Wolf, 2003; Mengel and Kirkby, 2006).

The available phosphorus (P) was of medium rates in the cultivated (8.56 ppm) and forested (7.35 ppm) soils. The exchangeable potassium (K) was high in both soil types, which is characteristic of the Mubi soils (Ekwue and Tashiwa, 1992; Tekwa and Usman, 2006; Tekwa and Belel, 2008). The sodium (Na) content was generally low ranging in both the cultivated (0.19-0.21 Cmol (+)/kg) and forested (0.22-0.37 Cmol (+)/kg) soils as reflected in the soils mild salinity levels (Table III). The calcium (Ca) content differed noticeably, a moderate rate (5.12 Cmol (+)/kg) was observed in the forested soil and lower rates (3.97 Cmol (+)/kg) in the cultivated soil. This variation could have been due to differences in crop consumption of Ca, leaching effects and physical degradation of the cultivated soils than it was on the forested soils.

Mg content of the soils were high, alongside the other basic cations, thereby yielding a very high percentage base saturation (PBS) in both the forested (93.66%) and cultivated (91.70%) soils. The result indicated impressive agricultural potentials of both soil types for variable crop supports (Wolf, 2003; Tekwa et al., 2006). Another student t-test comparison between the CEC content of forested and cultivated surface soil is presented in Table V. Since the calculated t-value (2.763) is greater than the t-critical (2.447), then Ho rejected, implying that there exist a significant difference (Pless than0.05) between the CEC content of forested and cultivated soils observed in this study. This occurrence is likely contributed by periodic accumulation of soil bases, characteristic of forest soils (Saviozzi et al., 2001).

Generally, the cation exchange capacity (CEC) recorded moderate (12.33 Cmol (+)/kg) in the forested soil and lowly (10.36 Cmol (+)/kg) in the cultivated soil. As it was with the OM content, the CEC amounts also statistically differed with significant differences (Pless than0.05) between the forested and cultivated soil types (Table IV). The relatively higher values of soil bases in the forested soil than on cultivated soil, possibly contributed to the higher CEC in the forested soil observed in this study. This adequate estimate of both the PBS and CEC certainly explains the relative potentials of especially the forested soils in contrast to the cultivated soils for sustainable crop production in the study area. This outcome similarly agreed with the earlier reports of Tekwa et al. (2006) for some soils within the same Mubi region. Likewise, it equally compares with the reports of Saviozzi et al. (2001), that long term corn production at an intensive level caused a marked decline in valuable soil qualities in Pisa, Italy.

CONCLUSION

The physico-chemical properties of the soils under test are still within ample crop support limits. The soil reaction (pH) and EC were moderate in the forested soil and lower in cultivated soil. The available P, soil porosity and bulk density were generally of medium rates, while K and Mg were all high in both soil types. Only PBS recorded very high rates in both soil types. Hence, the forested soil compared richer in nutrient stocks than the routinely cropped arable or cultivated field in the study area. It is recommended that the forested field should henceforth be converted into arable land-uses in order to utilize its high nutrient reserves. Also, the cultivated soils should further be supplied with soil fertilizing sources, such as organic and inorganic fertilizer materials, coupled with compatible crop husbandry practices capable of conserving the soils for sustainable crop production in the study area.

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I.J. TEKWA, B.H. USMAN+ AND H. YAKUBU

Department of Agricultural Technology, Federal Polytechnic, P.M.B. 35, Mubi, Adamawa State, Nigeria, Department of Soil Science, Federal University of Technology, P.M.B. 2076, Yola Adamawa State, Nigeria, Department of Soil Science, Faculty of Agriculture, University of Maiduguri, Borno State, Nigeria

To cite this paper: Tekwa, I.J., B.H. Usman and H. Yakubu, 2010. Comparative assessment of forested and cultivated soils for sustainable crop production in Mubi environment, Northeastern Nigeria. Int. J. Agric. Biol., 12: 749-753
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Publication:International Journal of Agriculture and Biology
Geographic Code:6NIGR
Date:Sep 30, 2010
Words:4644
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